This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Electron transfer dissociation (ETD) can be used to provide unique and complementary fragment ions when compared to other dissociation techniques, such as collision induced dissociation (CID). Weak side chain bonds such as are observed at phosphorylated amino acids in peptides are often lost during CID, but preserved during ETD. This makes the technique useful for the detection and analysis of posttranslational modifications in peptides and intact proteins. This project is devoted to the development and improvement of ETD for such applications.